17
/* compute an RSA modular exponentiation */
17
18
int rsa_exptmod(const unsigned char *in, unsigned long inlen,
18
19
unsigned char *out, unsigned long *outlen, int which,
19
20
prng_state *prng, int prng_idx,
28
29
_ARGCHK(outlen != NULL);
29
30
_ARGCHK(key != NULL);
31
33
if ((err = prng_is_valid(prng_idx)) != CRYPT_OK) {
35
if (which == PK_PRIVATE && (key->type != PK_PRIVATE && key->type != PK_PRIVATE_OPTIMIZED)) {
37
/* is the key of the right type for the operation? */
38
if (which == PK_PRIVATE && (key->type != PK_PRIVATE)) {
36
39
return CRYPT_PK_NOT_PRIVATE;
44
47
/* init and copy into tmp */
45
if ((err = mp_init_multi(&tmp, &tmpa, &tmpb, NULL)) != MP_OKAY) { goto error; }
48
if ((err = mp_init_multi(&tmp, &tmpa, &tmpb, NULL)) != MP_OKAY) { return mpi_to_ltc_error(err); }
46
49
if ((err = mp_read_unsigned_bin(&tmp, (unsigned char *)in, (int)inlen)) != MP_OKAY) { goto error; }
48
51
/* sanity check on the input */
54
57
/* are we using the private exponent and is the key optimized? */
55
if (which == PK_PRIVATE && key->type == PK_PRIVATE_OPTIMIZED) {
58
if (which == PK_PRIVATE) {
56
59
/* tmpa = tmp^dP mod p */
57
60
if ((err = tim_exptmod(prng, prng_idx, &tmp, &key->e, &key->dP, &key->p, &tmpa)) != MP_OKAY) { goto error; }
59
62
/* tmpb = tmp^dQ mod q */
60
63
if ((err = tim_exptmod(prng, prng_idx, &tmp, &key->e, &key->dQ, &key->q, &tmpb)) != MP_OKAY) { goto error; }
62
/* tmp = tmpa*qP + tmpb*pQ mod N */
63
if ((err = mp_mul(&tmpa, &key->qP, &tmpa)) != MP_OKAY) { goto error; }
64
if ((err = mp_mul(&tmpb, &key->pQ, &tmpb)) != MP_OKAY) { goto error; }
65
if ((err = mp_addmod(&tmpa, &tmpb, &key->N, &tmp)) != MP_OKAY) { goto error; }
65
/* tmp = (tmpa - tmpb) * qInv (mod p) */
66
if ((err = mp_sub(&tmpa, &tmpb, &tmp)) != MP_OKAY) { goto error; }
67
if ((err = mp_mulmod(&tmp, &key->qP, &key->p, &tmp)) != MP_OKAY) { goto error; }
69
/* tmp = tmpb + q * tmp */
70
if ((err = mp_mul(&tmp, &key->q, &tmp)) != MP_OKAY) { goto error; }
71
if ((err = mp_add(&tmp, &tmpb, &tmp)) != MP_OKAY) { goto error; }
68
if (which == PK_PRIVATE) {
69
if ((err = tim_exptmod(prng, prng_idx, &tmp, &key->e, &key->d, &key->N, &tmp)) != MP_OKAY) { goto error; }
71
if ((err = mp_exptmod(&tmp, &key->e, &key->N, &tmp)) != MP_OKAY) { goto error; }
74
if ((err = mp_exptmod(&tmp, &key->e, &key->N, &tmp)) != MP_OKAY) { goto error; }